Sinn Fein MP Martin McGuinness admitted he was the IRA gunman who sparked Bloody Sunday with a single shot, according to an informer, the Saville inquiry was told yesterday.

Christopher Clarke QC, counsel for the inquiry into the 1972 killings, revealed three security force documents detailing an informer's claims on Mr McGuinness's role in Londonderry at the time, and pleaded with him to give evidence at the inquiry. He has so far refused to offer a statement.

Mr McGuinness, minister for education in the short-lived power-sharing executive at Stormont, yesterday labelled the informer's allegations "a pathetic fabrication", a British military ploy to divert attention from the Parachute Regiment's killing of 14 civilians.

Sinn Fein said Mr McGuinness would welcome the opportunity to give evidence, although only last week he said he wanted to wait and see if Lord Saville's inquiry was a genuine attempt to get at the truth. He said then: "I have never hidden my past from anyone."

Mr Clarke, on the eighth day of his opening statement, disclosed a confidential document on the debriefing on an IRA informer, code-named Infliction. It was dated April 6, 1984. The crucial passage read: "Martin McGuinness had admitted to Infliction that he personally fired the shot from a Thompson sub-machine gun from Rossville Flats that precipitated the Bloody Sunday episode."

A classified message of May 15, 1984, sent to the RUC, Northern Ireland Office and the British embassy in Dublin, read: "Speaking in confidence, a leading member of the Provisional IRA who no longer has access to the organisation commented that Martin McGuinness personally fired the shot (from a Thompson machine gun on 'single shot') from Rossville flats in Bogside that precipitated the Bloody Sunday episode."

Another document said: "At the time of Bloody Sunday 30 January 1972, McGuinness was a senior member if not OC (officer commanding) of Londonderry PIRA. Although we have no collateral for the above report (the Infliction claim) there is intelligence that McGuinness was actively inolved in PIRA attacks in the city shortly after Bloody Sunday."

Paratroopers shot dead 13 unarmed Catholics, seven of them teenagers, during an illegal anti-internment march in Derry on January 30, 1972. A man who was wounded died five months later.